Temperature control apparatus



Jan. 8, 1952 G GADms 2,581,525

TEMPERATURE CONTROL APPARATUS Filed July 17, 1948 7' E MP5 1717 7" 0/75 RESPO/YSI VE zoo ZSnnentor Z GEMS 7f 6/7001? (Ig orneg Patented Jan. 8, 1952 I 2,581,525 TEMPERATURE CONTROL APPARATUS Gene '1. Gaddis, Minneapolis, Minn assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application July 17, 194s, Serial No. 39,350

Claims.

The present invention relates to control apparatus and particularly to that type of control apparatus adapted for use in temperature control wherein it is desired to maintain a constant temperature within a given space under varying heat demand or load demand conditions.

In some present day heating systems it is customary to employ heating panels of the type that accomplish heating by radiation and convection. As these panels generally cover an entire wall surface or ceiling surface it is necessary to provide some method of modulating the heat flow to the panel in accordance with the load conditions which may be functions of such factors as outdoor temperature, room size, ther-.

mal heat loss, outdoor wind velocity and many others. The heating panel may be constructed of a number of heating elements that may be energized in accordance with existing load conditions. It is therefore desirable to energize only those elements needed to maintain the temperature within the space to be heated at a desired value. I

The present invention is concerned with a control apparatus which is adapted to control the heating elements of a heating panel by continuously energizing a. certain number. of the heating elements in a series and periodically energizing the heating element next in series all in accordance with the load conditions determined by any desired type of heating load measuring apparatus.

It is therefore an object of the present invention to provide an improved control apparatus which will periodically energize a condition maintainin element for time periods determined by a condition load measuring device.

A further object of the present invention is to provide a control apparatus which will, when a predetermined load condition exists, energize continuously a series of a condition maintaining elements and energize periodically the next condition maintaining element in the series of elements in accordance with the load condition then existent.

Still another object of the present invention is to provide an electronic control device which is operable to cycle on and off a condition maintaining element in accordance with the voltage that exists in the input to the control apparatus. r

A still further object of the present invention is to provide an electronic control apparatus which is rendered inoperative and operative in accordance with the charging and discharging rate of condensers whose charge is established by load condition measuring apparatus to energize a means for maintaining a desired temperature within a given space.

These and more detailed and specific objects will be disclosed in the course-of the following specification, reference being had to the accompanying drawing on which is a diagrammatical showing of a heating panel, a temperature load condition measuring apparatus and the control circuit of my invention connected operatively thereto.

Referring to the single figure, the numeral Ill represents a heating panel which may be of the type utilizing steam as the heating source. Steam may be supplied to the heating panel by a plurality of conduits l I, l2 and I3. Controlling the flow of steam to the heating panel ID are suitable electrical valves ll, l5 and I6 associated with the respective conduits H, l2 and I3. The numeral I'l represents the heat demand indicating apparatus of any desired type which will have on its output terminals a voltage representative of the amount of heat that must be added to a space being heated to maintain a constant temperature. A thermal responsive bimetal A and associated contacts l8 and H! are I provided for maintaining the control apparatus I consisting of a primary winding 2| and a secondary winding 22, supplies power to one section 23A of a double triode vacuum tube 23 which consists of an anode 24, a control electrode 25, and a cathode 26. The second section 23B of the twin triode 23 consists of an anode 21, a control electrode 28 and a cathode 29. Located in the energizing circuit of the second section of the twin triode is a relay 30 having a relay energizing winding 3|, a pair of switch blades 32 and 33 biased. by means not shown, so that the blade 32 engages a switch contact 35. A second pair of contacts. 36 and 34 are provided for contacting switch blades 32 and 33 respectively, when the relay is energized. Potentiometers 31, 38, 39v

and resistor 40 are provided for variably charging and discharging a pair of associated condensers 4| and 42. Potentiometer 43 is a bias-- 3 trode 41, and a cathode 48 while in the right hand section 4513, it consists of an anode 48, a control electrode 50, and a cathode 5i; Associated with'thecinput circuit of. theleft hand section 45A oi?v the dual triode 45v are potentiometers 52, 53 and 54 which cooperate with condenser 55 to establish the bias potential between control electrode -41 and cathode 48.

Associated with the right hand section 45B of the dual triode 45 is a resistor 59and potentiometers 51, 58 and 60, all of which co,op-..

erate with condenser 6| to establish the biasingpotential on the right hand sectionof the dual triode 45. A relay 10 consists of arelay wind ing H and a switch blade 12 biased out of engagement with contact 13 by means not shown.-

A coupling relay,15 consists of a relay winding 16, switchblades 11, 18 and 18 biased respectively into engagement with contacts 80, 8| and 82 by. means not shown. Contacts 83,84 and 85 are provided for association with'switch blades 11,

switch contacts I88 and I88. I13 and I81 are associated with switch blades I88 and I90 respectively when relay I10 is energized..

For purposesioi simpliflcation a third stage associated'with'my control apparatus is shown in block diagram form with only that portion of the diagram shown that is directly associated with the-'previous-stages'. The numeral 200 represents the temperature responsive section of my control apparatus while the numeral 205 represents the a timing or couplingsection of my control appa- 18 and 18 respectively when relay15 becomes I energized.

The second electronic circuit in the series of control circuits of my invention is almost iden tical to that which has already been described will be well to keep in mind that my controlapratus. The output relay 230 corresponds to relay 1 30 of stage l'andrelay I30 of stage 2 and may be seen to consist. of a relay winding 23I having a switch blade 233 normally-biased out 01 engagementwithits associated contact 234. A timing relay 210 corresponds in part to relays 10 and I10 and may be seen to consist of a relay winding 2' and a' switch blade 288 biased into engagement with anassociated switch contact 286. -Supplying direct current power and biasing voltages for all of my control apparatus is a suitable power supply carrying the reference numeral 2 I0.

Operation Indiscussing the operation of my invention, it

paratus is for'modulatingly controlling theenergization of the heating panel I0. For purposes of illustration, assume that for light load conditions it is desirable to supply steam to panel I0 I22, supplying energy to the left-hand section I23A of a dual triode I23. The triode section I23A may be seen to consistfoi" an'anode' I24, a control electrode I25 and a'cathode I26. The right hand section I233 of dual triode I23 may be seen to consist of an anode I21, a control electrode I28, and a cathode I29. Connected in the output of triode I23B isa relay I having an energizing winding I3I and associated switchblades I32. and I33 with switch-blade I33 biased through conduit periodically and that for medium load conditions it will be necessary'to supply steam continuously to panel I0 through conduit I I and periodically through conduit. I 2. Similarly," assume that forheavy load conditions, it

I is desirable to supply steam to conduit II and out of contact with its associated contact I34 and switch blade I32 biased intoengagement with contact I35. A switch contact I36 is as-' sociated with blade I32 when relay I30 is energized. The input circuit to triode I23B consists of a pair of potentiometers I31 and I38 associated with a resistor I40 and a pair of condensers MI and I42. The potentiometer I43 is associated with "the input circuit to the triode I23A. Afurther dual triode I45 consists of a left-hand triode section I45A having an anode I46, 2. control electrode I41, and a cathode I48 and a right hand triode section I45B having an anode I49, a control electrode I50 and a cathode I5I'. Associated with the input to amplifier I45A are potentiometers I52, I53 and I54 which cooperate with a condenser I55 for biasing triode I45A intoand out of conduction. The input section to triode 53 consists of potentiometers I51, I58, and I associated with a resistor I59 and a condenser I6I for regulating the conductivity of the'triode I453. The output relay for triode I45 is relay I62 having a relay winding I63 and an associated switch blade I64 biased out of engagement with its associated contact I65. The output relay for the triode section 53 is a relay I66 having a relay winding I81 and an associated switch blade I68 which is normally biased out of engagement with its associated switch contact I63. A timing control relay I10 consists of a relay winding "I having a pair of switch blades I89 and I90 normally biased into engagement with a pair of conduit I2 continuously while supplying steam periodically through conduit I3.

The light load conditions-will be considered first, thatis when steam is periodically supplied to panel I0 through conduit II only. The heat demand indicating device I1 associated with my invention isipreferably or the type which has a voltage output representative of the amount of heat that must be supplied to maintaina constant temperature within a given space. With this, it will be assumed that the voltage on the output terminals when measured from ground 300 to terminal 30I will become more negative with increases in demand for heat. Assuming further that when the relays on the diagram are in the position shown, the voltage appearing across the terminals of indicator I1 is applied to the input circuit to'tube 23A to operatively bias the same in accordance with the voltage on the output terminals of the demand indicator I1. This circuit may be traced from the terminal 30I through conductors 302 and 303, switch contact 80, switch blade 11, and conductor 304 to control electrode 25 of triode 23A. The current flow circuit for triode 23A may be traced from the left hand terminal of the secondary section 22 through conductor 305, anode 24, cathode 26, conductor 306, resistor 40 and conductor 301 back to the right hand terminal or secondary 22. The amount of current flow through this last traced circuit will be a function of the voltage that is appearing upon the control electrode 25 which, as explained above, is biased by demand indicating means I1. The current flow through the triode 23A in flowing through the resistor 40 serves to place a charge on the condenser 42 such that its left hand terminal is positive and its right hand ter- Switch contacts and a negative. The magnitude of this voltage will be 'a'iunction of the conductivity of the triode 23A. 7

The charge on condenser 42 is directly associated with the biasing circuit for triode 233. The plate current circuit for triode 238 may be traced from the terminal 303 or the power supply 2|l through conductors 309, 3|0 and 3| I, relay winding 3|, conductor 3|2, anode 21, cathode 29, and ground 3|! back to ground terminal 314 of the power supply. Assume that the relay 30 has just become energized by current flowing in the last trace circuit and the switch blade 32 has moved into engagement with switch contact 33. "At the instant this occurs the condenser 4| which is connected directly between the cathode 29 andcontrol electrode 28 has a charge on it which permits the current now through triode 23B to energize the relay 30. With relay 30 energized as in the above traced circuit a charging path for condenser 4| is established from the condenser. and this circuit may be traced from the right hand terminal of the condenser 42. through conductor 3|5, potentiometer 31, conductor 3|,6, switch blade 32, and conductor 3|1 to condenser 4|. Since there is resistance in the last traced charging circuit for condenser 4|, there will be a time delay in the charging of this condenser which will depend upon the setting of the tap of the potentiometer 31. When condenser 4| starts to charge it will become more negative on its upper terminal and tend to bias the control electrode 28 more negative. Due to the difierential between the current flow required to energize relay 30 and the current flow required to maintain the relay energized it is possible to shift the bias of triode 233 over a certain voltage range without deenergizing relay 30. The time that it takes the charge on condenser 4| to shift from the relay energizing point to the relay drop out point will depend upon the resistance of potentiometer 31 and the capacity of capacitor 4| as well as the charge on condenser 42. As soon as the condenser 4| has been charged sumciently negative the current flow in triode 23B will drop below the relay 30 current holding point and relay 30 will become deenergized.

When relay 3|) becomes deenergized the switch blade 32 moves into engagement with switch contact 35 to establish a discharge circuit for condenser 4|. The discharge circuit for condenser 4| may be traced from the upperterminal of condenser 4| through conductor 3| 1, switch blade 32, switch contact 35, conductor 3|3; resistor 33, conductor 3| 9, bimetal "A, which under conditions calling for operation of the heating panel I is engaging switch contact l8, ground conductor 32|l and ground 3|3 back to. the lower terminal of the condenser 4|. It will be noted that in the last traced circuit there is a potentiometer 33 which has a variable tap which may be used to determine the rate of discharge of the condenser 4|. As soon as the condenser 4| has discharged sufiiciently the control heating panel. As explained above, the voltage output on terminal 3M will become more negative upon greater demand for heat. This more negative signal will bias the triode 23A to be less conductive than previously. With the triode 23A conducting less there will be a smaller direct current charge built up on the condenser 42. With a smaller charge on condenser 42 the relay 30 will be maintained in the energized position longer since it will take longer for the condenser 4| t6 charge to a point where it will drop the conductivity of the triode 23B below that required to maintain relay 30 energized. Each time the relay 30 is lnoved into the energized position the switch blade 33 moves into contact with its associated contact 34 and completes an energizing circuit for the steam valve 4. The circuit to this valve |4 may be traced from the input power line 32| through conductor 322, switch contact 34, switch blade 33, conductor 323, conductor 324, and valve |4 back to the other input power line325.

From the foregoing, it can be seen that when the demand indicating device 11 is operating in a range of values between light load and moderate load, the relay 30 and the steam valve l4 will be cycled on and off for time periods whose lengths will be dependent upon the output signal from the indicator |1. As soon as the demand indicating device |1 indicates that there is need for more heat than can be supplied by the periodic operation 'of the steam valve I4 a timing or coupling stage comes into operation. This timing stage is directly concerned with the triode stage 45A and triode stage 453 and the operating circuits therefore. This timing stage is so interconnected with the control apparatus that it will be operative to cause continuous operation of the relay 30 and initiate periodic operation of relay I30 in the second stage of operation.

In discussing the operation of this timing stage, it will be assumed that the triode 45B is conducting so that a plate current circuit may be traced from the terminal 308 of the power supply 2|0 through conductor 3B9, conductor 3), conductors 326 and 321, relay winding 61, anode 49, cathode 5|, and ground 328, back to ground terminal 3|4 of the power supply. With triode 45B conducting, the relay 66 will be energized and the switch blade 68 will be moved into engagement with its associated contact 69. The triode 45A will be assumed to be nonconducting; this is because the control electrode 41 is connected effectively directly to the biasing terminal 329 of the power supply 2 0. This circuit may be traced from the terminal 329 through conductors 333, 33| and 332, potentiometer 52, and potentiometer 53 to control electrode 41. The actual bias on the tube 45A will be dependent upon the position of the tap of the potentiometer 52. The triode 45A will remain effectively nonconducting until the biasing voltage on the triode is altered. The altering of this biasing voltage is accomplished by the relay 1!] which is energized when the steam valve H is energized. The energizing circuit for this relay 10 may betraced from the input power line 32 conductor 322, switch con tact 34, switch blade 33, conductors 323 and 333, relay winding 1| and conductor 334 back to the other input power line 325. When relay 10 becomes energized the associated switch blade 12 is moved into engagement with contact 13 to establish a discharge" circuit for the condenser 55 which is actually the biasing condenser for triode 45A. The discharge circuit may be traced accuse from the upper terminal of the condenser through the potentiometer 54, switch contact 13, switch blade 12. conductor 335 back to the lower terminal of condenser 55. With the discharging circuit for condenser 55 established, a further voltage divider network is provided for the biasing voltage supply from the power supply 2H0. This voltage divider network actually consists of the potentiometers 53 and 54 in series so that now, with relay energized, the voltage across condenser 55 will eventually discharge from the value that was established solely by potentiometer -52 to a value that will be established by the voltage divider consisting of potentiometers- 53 and 54.

As soon as the condenser'55 has discharged to the new point established by the voltage divider the tube 45A will become conductive. The time that it takes for condenser 55 to discharge will be dependent upon the RC time constant of the condenser 55 and the resistor potentiometer 54. This time constant is so chosen that it will not permit condenser 55 to discharge below the relay energizing point until it is necessary to bring into winding 63, anode 46, cathode 48, and ground 328 back to ground 3 I4 of the power supply. With triode 45A conducting sufiiciently the relay 62 will become energized and the switch blade 84 will move into engagement with its associated switch contacts 65. When switch contact 65 engages switchblade 64 an energizing circuit is established to the coupling relay 15. This energizing circuit may be traced from the input power line 32I through conductors 331, switch blade 68, switch contact 69, conductor 338, switch contact 65, switch blade 64, conductor 339, relay winding 16, and conductor 340 back to the other input power line 325. r

When relay becomes energized the switch blades 11, 18 and 19 move into engagement with their associated switch contacts 83, 84 and 85 respectively. When the switch blade 11 engages contact 63 a new biasing circuit is established for the triode 23A. This biasing circuit may be traced from the biasing terminal 329 of the power supply 2I0 through conductors 330 and 33I, potentiometer 43, switch contact 83, switch blade 11 and conductor 304 to control electrode 25. This biasing voltage is so chosen as to render the triode 23A effectively nonconducting. With the triode 23A efiectively nonconducting, the voltage that was formerly on condenser 42, due to the current flow through triode 23A, will not be present so that the triode 233 will have no voltage to move the control electrode below the relay 30 drop but point. This means that the relay 30 will remain energized with switch blade 33 engaging switch contact 34 and maintaining a the steam valve I4 continuously in operation.

The apparatus is now in a position to permit periodic operation of the second stage at steam valve I5. The control circuits eflecting the energization of the steam valve I5 are almost identical to those employed in the. first stage for energizing steam valve I4. There is one 'main ditierence in the operation of the control circuits for the first stage and the control circuits for the second stage and that is that the time constant of the RC timing networks are so chosen that the second stage is operative periodically only over a middle range of load demand signals from the indicating device I 1.

The controlling signal for the second stage 01 operation originates from the load indicating device I1 and is coupled to the control electrode I of the triode I23 by a circuit that may be traced ,from the terminal of indicatorv I1 through conductors 302, 34H and 342, switch contact I80, switch blade I11, and conductor 343 to control electrode I25. The conducting circuit for the triode I23A may be traced from the left hand terminal of the secondarywinding I22 through conductor 344, anode I24, cathode I26, resistor I40, and conductor 345 back to the right hand terminal of the secondary section I20. The flow of current through the resistor I40 in the last traced circuit results in a charge being placed on condenser I42, which charge will have a magnitude dependent upon the conductivity of the triode I23A. The charge on the condenser I42 is effective to bias the triode I23B into and out of conduction in accordance with the charging and discharge time of the condenser I4I, which isconnected directly across the control electrode-cathode circuit of the triode I23B.

The charging circuit for the condenser I4I may be traced from the right hand terminal of the condenser I42 through potentiometer I31, conductor 346, switch contact I36, switch blade I32, and condenser I4I back to the left hand terminal of condenser I42. The discharge circuit for condenser I4I may be traced from the upper terminal of condenser I4I through switch blade I32, switch contact I35, potentiometer I38, ground 348, and ground 341 back to the lower terminal of the condenser I4I. The energizing circuit for the triode I23B may be traced from the terminal 308 of the power supply 2I0 through conductors 309, 349. and 350, relay winding I3I, anode I21, cathode I29, ground 341, and ground 3 of the power supply. It will be noted from the above discussion thatwhen the relay I30 is energized and the switch blade I32 is moved into engagement with switch contact I36, the condenser I will be charging through potentiometer .I31 so that its time of the condenser MI and thereby regulate the off time of the relay I30.

Also energized when the relay I30 is energized is the steam valve I5 whose energizing circuit may be traced from the input power line 35I through switch contact I34, switch blade I33, conductor 352, switch contact 85, switch blade 19,

conductor 354. switch blade 18, switch contact 84,

conductor 353, and steam valve I5 back to the other input power line 355. It will be noted that the steam valve circuit may be completed only when the coupling relay 15 is in its energized position since this coupling relay prevents the steam valve l5 from cycling periodically until there is avenues continuous operation of the steam valve I4. From the foregoing, it can be seen that the relay I38 will cycle the steam valve I on and of! at a rate determined by the load demand indicated by the indicator II- and this cycling will become effective only when there is continuous operation in the first stage of the heating system.

Should the demand indicating device I1 be indicating a load that calls for continuous operation of the first and second stages and periodic operation of the third stage it is necessary to bring into operation the second timing stage and coupling stage the former of which consists of the dual triode I45 and its associated circuits and the latter of which consists of the coupling relay I15. In first observing the operation of the timing stage, it will be assumed that the triode section 53 is conducting so that the relay I86 located in the plate circuit of the triode M513 is energized. The plate circuit for the triode section I 45B may be traced from the terminal 308 of the power supply 2I0 through conductors 309, 349, 356 and 351, relay winding I61, anode I49, cathode I 5I and ground 358 back to ground terminal 3I4 of the power supply. With relay I66 energized the switch blade I68 will be engaging switch contact I69.

It will further be assumed that the triode section I 45A is efiectively non-conductin and its associated plate relay I62 is not energized. This will be because the grid I41 of the triode SA is biased below the relay energizing point by a connection directly to the bias supply of the power supply 2| 0. This circuit may be traced from the terminal 329 of the power supply through conductors 330, 358, 359, 360 and 36I, potentiometer I52, and potentiometer I53 to control electrode I41. As long as the potentiometer I54 is not connected across the condenser I55, the condenser I55 will have a biasing volta e on it that will be dependent upon the position of the tap on potentiometer I52. This biasing voltage will maintain the current flow in the triode I45A below the relay energizin point.

The potentiometer I54 is connected across the condenser I55 whenever the steam valve I5 is energized by the relay I30. This is accomplished by the relay I whose energizing circuit may be traced from the input power line 355 through relay winding I1I, conductor 353, switch contact 84, switch blade 18, conductor 354, switch blade 19, switch contact 85, conductor 352, switch blade I33, and switch contact I34 back to the other input power line 35I. When relay I10 is energized, the switch blade I89 and I90 move into engagement with contacts I13 and I81 respectively. This will complete a discharge circuit for the condenser I55 that may be traced from the upper terminal of condenser I55 through potentiometer I54, switch contacts I13, switch blade I89, conductor 362, switch blade I90, and switch contact I81 back to the lower terminal of the condenser I55. The potentiometer I53 and potentiometer I54 now form a voltage divider which will establish a new biasing voltage for the control electrode I41 to which it will be necessary for the condenser I55 to discharge to. The discharging time of the condenser I55 is so selected that the condenser will not discharge sufliciently to bias the triode I45 to the relay energizing point until the steam valve I5 remains energized for a length of time indicating there is need for an additional stage to be brought into operation. When the steam valve does remain energized for a predetermined length of time, the condenser I will be discharged sufllclently to bias the triode I45 to the relay energizing point. The plate current circuit for the triode I45A may be traced from terminal 308 oi power supply 2I0 through conductors 309, 349, and 356, relay winding I83, anode I43, cathode I48, ground 358 back to ground 3I4 oi the power supply. When the plate current reaches a certain value in the last traced anode circuit, the relay I62 will become energized and will move switch blade I84 into engagement with switch contact I65. With switch blade I64 engaging switch contact I65 an energizing circuit will be completed to the coupling relay I15 which may be traced from input power line 355 through conductor 368, switch blade I88, switch contact I69, conductor 365. switch contact I65, switch blade I64, conductor 364, relay winding I16 and conductor 863 back to the other input power line 35 I When the coupling relay I15 becomes energized, the switch blades I11, I18 and I19 move into engagement with their associated contacts I83, I 84 and I85 respectively. When switch blade I 11 engages switch contact I83, a new biasing circult is established for the triode I23A to eiiectively cut the tube oil, or below the current conductive point. This new biasing circuit may be traced from the terminal 329 of the power supply 2I0 through conductors 330, 358, 359, and 361, potentiometer I43, switch contact I83, switch blade I11, and conductors 343 to the control electrode I25. When there is no current flow through the triode I23A there will be no biasing voltage placed on the condenser I42 so that when the relay I 30 is energized the control electrode I28 will be effectively at cathode potential and the triode I23B will continue to pass current and maintain relay I30 energized continuously which will mean that the steam valve I5 will now be operating continuously.

With the second stage steam valve I5 operating continuously, it is desirable to permit periodic operation of the third stage steam valve I6. For purposes of simplification, the third stage of operation has been shown in block diagram form,

but in actual practice the third stage would be constructed identically to the second stage of operation withthe RC time constants of the timing circuits altered so that the demand indicating device I1 would be operative to cycle a third stage on and off only when there is a large demand for heat.

The relay 230 in the third stage of operation corresponds to the relay I 30 in the second stage of operation and is operative when energized to move the switch blade 233 into engagement with the associated contact 234. This will complete an energizing circuit for steam valve I6 that may be traced from the input power line 368 through switch contact 234, switch blade 233, conductor 369, switch contact I85, switch blade I19, conductor 310, switch blade I18, switch contact I84, conductor 31I, and steam valve l6 back to the other input power line 312. As in the case with the steam valves I4 and I5, the steam valve I6 will be cycled in accordance with the signal that is sent from the demand indicating device I1 whose circuit may be traced from the terminal 3III through conductors 302, 34I, 313, and 314 to the stage 3 temperature responsive section 200. The power supply for the temperature responsive stage 200 may be traced from the power supply from terminal 308 through conductors 309, 316 and 311 to the temperature responsive device 200 to ground terminal 315 and back to the ground assua e terminal 3I4 of the power'supply. The biasing;

voltage for the third stagealso originates in th power vsupply 2I6 and may'be traced from the terminal 329 through conductors 336, 358, 318 and 319 to temperature responsive section 266.

cter is so chosen that the RC1 time constant of the potentiometer I58 and the condenser I8I will not permit the current flow in'the triode I453 to drop below, the current flow necessary to main- In the event that it is desired to have additional, stages of operation, it is necessary to provide a timing. and coupling circuit in thethird stage-which isshown asnumeral 265 in block diagram form andcorresponds identically to the timing and-coupling stage of stage 2. is

shown to be operatively interconnected with the temperature responsive sectionof stage 3 by conductors 386 and 38I andto-be connected to the power supply 2 I 6, conductors 316- and318 by conductors. 382 and 383. In theevent that a fourth stage were provided,v it would be operatively inter-connected with stage 3 so that stage 3 would be rendered operative continuously while the fourth stagewas operating periodically, in

the same manner as occurs-between the contintain relay I66 energized until it is desired to discontinue operation entirely in the third stage of operation. This willoccur when the time periods or operation of the third stage have dropped below a predetermined value. This may best be understood by noting that condenser I6I hasa discharge [circuit through potentiometer I66 which will, discharge the condenser I6I when the rela'y216 is energized. ,When, the relay 216 is deenergized, the condenser IN is charged through the potentiometer I58 so that it will tend to bias the tube 1453 in a direction to decrease thecurrent flow through the tube below the point necessary to maintain relay I66 energized. The time that relay 216 is deenergized is always constant sincethle of! periods of operation are constant as explained above. As soon as'the relay 216 becomes energized again,".the charging circuit for condenser I6I will be broken and it will start to discharge through the potentiometer I 66. If

the time the relay m is energized is relatively short, the condenser I6I will nothave fully discharged and the subsequent deenergization oi relay 216 and theresultant completion of the first stage moves from operating periodically to,

operating continuously withthe second stage operating periodically. And further, the second stage was considered to be operating continuously and the thirdstage operating periodically. It is now necessary to consider the operation'oi, the apparatus when the load indicating device I1v is decreasing its demand for heat which will mean that it is desired to discontinue operation of-certain of the heating elements that have been.

already energized. Let it be assumed that the steamvalve I4 and steam valve I5 are operating continuously and that the steamvalve I6 is being energized periodically. The, decoupling with the steam valve I6 operating periodically will be initiated by the relay 216 which will be operating periodically since the relay 216 is connected directly across the power line supplying energy to the steam valve I6 so that when the steam valve I6 is energized the relay 216 is energized. When the relay 216 is deenergized, the switch blade 288 moves into engagement with switch contact, 286 to complete a circuit in the decoupling stage of the second stage timing circuit common to the input of the triode, 53. Up to this time it has been assumed that the triode I45B has been continuously conducting, when the relay 216 is deenergized, switch blade 288, closing with switch contact 286, completes a new biasing circuit for the triode I 45B that may be traced from the terminal 329 of the power supply 2I6, through conductors 336, 358, 359, 866, and 384, potentiometer I51, potentiometer I58, conductor 385, switch contact 286, switch blade 288, conductor 386, to the control electrode I56. It will be noted that the condenser I6I is connected directly across the input or control electrode cathode circuit of the triode 53 so that it efiectively establishes the biasing potential of the triode 53. It will be further noted that the last traced biasing circuit from the power supply 2I6 through relay 216 includes a potentiometer I58. The resistance of this potentiomcharging circuit Iorcondenser I6I will permit the condenser to charge to a point where it will bias triode 'I45B belowthe point necessary to maintain relay I66 energized.

When the relay I66 becomes deenergized the switch blade I68 will move out of engagement with its associated switch contact I 69 to open the energizing circuit for the coupling relay I15.

When the coupling relay I15 becomes deenergized the biasing circuit for the triode I23A is switched back to the load demand indicating device I6 by movement of the switch blade I11 into engagement with switch contact I86. 'When switch blades I18 and I19 move out of engagement with theirlassociated switch contacts I84 and I85, respectively, the energizing circuit for steam valve I6 will be open so that 'itfwill be impossible to energize the steam valve I6 until the relay I15 is once again energized.

Deenergization of the relay I15 effectivelycon-- nects resistor I59 across the input circuit to the triode I453. This circuit may be' traced from the lower terminal of the resistor I59 through conductor 381, switch contact I82, switch blade I19, conductors 316, switch blade I18, switch contact I8I, and ground 341 to ground 358. With the resistor I59 connected in parallel with the potentiometer I66, a new voltage divider network is established across the input to the triode I45B so that the bias voltage from the power supply 2I6 will now be divided across the potentiometer I58 connected in series with the parallel combination of resistor I59 and potentiometer I66. This new biasing voltage across the resistor I59 and potentiometer I66 is also placed across the condenser I6I and is of such a value that it will permit the current flow through the triode 53 to reenergize the relay I66. There will be a certain amount of time delay involved from the discharging of condenser I 6| through the parallel combination of resistor I59 and potentiometer I66 which is necessary to permit the condenser I55 associated with the input of triode I45A to discharge below the point necessary to maintain relay I62 energized. As explained above, it will be seen that the potentiometer I54 will be disconnected from the discharging circuit for condenser 13 I55 when-the relay I18 is deenergized. It will be seen that the relay I52 must be deenergized before relay I55 is again energized to permit the coupling stage from becoming operative again. This is taken care of by providing an operating differential between the point of operation calling for periodic operation in the third stage and the point calling for periodic operation in the second stage. In other words, the relay I55 will become deenergized only when a load demand signal is impressed which will maintain the operation of the second stage for periods of time less than that required to energize relay I52. The time delay of the condenser II discharging through the parallel connected resistor I59 and potentiometer I68 is such that the second stage will have gone through an operating cycle so that the charge on condenser I55 will have been altered. by the connection to the bias supplied through contacts of relay I18, to shift the bias of triode 5A below the point necessary to maintain relay I52 energized. With relay I52 deenergized, the switch blade I54 will move out of engagement with its associated contact I55 to maintain the energizing circuit for the coupling relay I inoperative when the relay I55 once again becomes conductive after the condenser I5I has discharged to the relay current biasing energizing point.

With relay I52 deenergized, the apparatus will be operating under that range of values where the second stage will be cycling on and ofl periodically and the first stage will be operating continuously.

In the event that there is a further decrease in demand for heat indicated by the indicator I1 such that it is desirable to operate only the first stage periodically, it will be necessary to decouple the second stage from the first and this is accomplished in practically the same manner as the third stage was decoupled from the second. Like relay 218, the relay I18 is a decoupling relay which, when in the deenergized position, moves switch blades I89 and I98 into contact with their associated contacts I85 and I88 to complete a biasing circuit for the control electrode 58 of the triode 453. This biasing circuit may be traced from the terminal 329 of the power supply 2I8 through conductors 338, 33I, 332, and 388, potentiometer 51, potentiometer 58, conductor 389, switch contact I85, switch blade I89, conductor 352, switch blade I98, switch contact I88, and conductor 398 to the control electrode 58. This last traced circuit, like the corresponding circuit of the input to triode 5B is completed through the potentiometer 58 whose resistance when cooperating with the conductor 5| forms an RC timing network which will function to bias the triode 45B below the point required to maintain the relay 55 energized.

Normally, the condenser 5I will discharge through the potentiometer 58 when the biasing circuit is not connected to the control electrode However, as soon as the on time of the and steam valve I5 the biasing circuit will be connected long enough to the control electrode 58 so that the condenser 5| will be charged to a biasing voltage which will cut the current flow in triode 45B below the point necessary to maintain relay 55 energized. When relay 55 becomes deenergized the switch blade 58 moves out of contact with its associated switch contact 59 to,

open the energizing circuit to the coupling relay 15.

When the coupling relay 15 becomes deenergized, the biasing circuit on the triode 23A is connected back to the temperature load indicating device I1 by a switch blade 11 engaging the associated switch contact 88. Also deenergized, when the coupling relay 15 becomes deenergized, is the energizing circuit to the steam valve I5 since the switch blades 18 and 19 move out of engagement with switch-contacts 84 and 85, respectively. When switch blades 18 and 19 engage their deenergized contacts 8| and 82 respectively a voltage divider network is connected into the biasing circuit of the triode 45B by connecting the resistor 59 in parallel with the potentiometer 58. This parallel connection may be traced from the resistor 59 through conductor 39I,

switch contact 82, switch blade 19, conductor switch blade 18, switch contact 8|, to ground 392 back to ground 328. With the resistor 59 connected in parallel with the potentiometer 68, the condenser 5I will tend to charge to a value that will bias the triode 453 to a point where the relay 55 will once again become conductive. As was the case with relay I52 and relay I55, the relay '52 must be deenergized before the relay 55 is again energized to permit the coupling stage from becoming operative. As explained above, this is taken care of by providing anoperating differential between the point of operation calling for periodic operation of the second stage at the point calling for periodic operation only in the first stage. In other words, the relay 65 will become deenergized only with a load demand signal present which will maintain the operation of the first stage for periods of time less than that required to energize relay 52. The time delay in the condenser 5I discharging through the parallel resistor 59 and potentiometer 58 is such that the first stage will have gone through an operating cycle so that the charge on condenser 55 will have been altered, by the connection to the bias supplied through the contacts or relay 18, to shift the bias of triode A below the point necessary to maintain relay 52 energized. When the relay 52'becomes deenergized, the switch blade 54 moves out of engagement with its associated contact 55 to maintain the energizing circuit for the coupling relay 15 deenergized when the relay 66 once again becomes conductive. The control apparatus is now operating periodically in the first stage and is not operating at all in either the second or the third stages.

When the load condition indicated by indicator I1 no longer exists, it is desirable to provide some means of discontinuing operation of the apparatus. This may be accomplished by the bimetal "A which is operable to move into engagement with contact I8 when there is a demand for heat and into engagement with contact I9 when there is .no demand for heat. The operation as discussed so far has assumed that the bimetal has been engaging contact I8. With the heating demand non-existent and the bimetal I1A engaging contact I9 the biasing circuit of the power accuse through conductors 330 and 393, potentiometer 39.

switch contact i9, bimetal i1, conductor M9, potentiometer 38, conductor SIB, switch contact 35. switch blade 32, and conductor 3ii to control electrode 26. This biasing potential maintains the current flow in the triode 23B below that point necessary to energize relay 3!] and will maintain triode 23B so biased until such time as the bimetal i'IA once again moves in the heat demanding direction and contacts contact iii to form the discharging circuit for the biasing condenser 4 l.

From the foregoing it can be seen that a control apparatus has been provided for eifectively modulating the heat flow through a heating panel in accordance with the demand, for heat. It can be further seen that the control apparatus has been provided to cycle into operation a series of heat controlling devices to maintain a constant temperature within a given space.

Although I have discussed my invention in connection with a particular type of steam heating panel, and while it is particularly well adapted for use there, it will be obvious to those skilled in the art that my invention could be applied to any apparatus where it is desirable to modulatingly control a condition in accordance with load demand indicating means. Therefore, I intended to be limited solely by the scope of the appended claims, in which I claim:

1. A condition control device comprising in combination, a plurality of load control devices, load demand sensing means, means interconnecting said load sensing means and said loadcontrol devices so that sensing means is operable to energize said load control devices, a plurality of coupling means, and means connecting said coupling means in between each of said load control devices so that said coupling means is operable to maintain each successive device of said load control devices operating periodically and all preceding of said devices operating continuously in accordance with the load demand indicated by, said load sensing means, each of said control devices including circuit means controlled by said load demand sensing means modulatingly varying the periodic operation of said devices.

2. A condition control apparatus comprising in combination, a load condition sensing means, a plurality of interconnected condition control devices each adapted to energize periodically or continuously condition changing means, each of said control devices including circuit means controlled by said load demand sensing means modulatingly varying the periodic operation of said device, means interconnecting each of said condition control devices and said sensing means, a plurality of coupling means, and means connecting a separate one of said coupling means between each of said condition control devices and being operable to energize each succeeding of said condition control devices eriodically when the condition control device preceding said coupling means is operating continuously.

3. A condition control apparatus comprising in combination, a load condition sensing means, a plurality of interconnected condition control devices each adapted to energize periodically or continuously condition changing means, means interconnecting each 01' said condition responsive devices and said sensing means, a plurality of coupling means, means connecting said coupling means between each of said condition control 16 devices and being operable to energize each succeeding of said condition control devices periodically when the condition control device preceed- 'ing said coupling means is operating continuousor continuously, means connecting said load condition sensing means to each of said condition control devices so that each of said condition control devices is operable in periods of modulatingly increasing length for increases in load measured by said sensing means, means common to each of said condition control means to initiate energization of each of said control means periodically for different ranges of load, coupling means, and means connecting each of said coupling means between each of said condition control devices to maintain each of said control devices preceding said coupling means operative continuously when the load condition has exceeded the periodic operating range for said preceding responsive device.

5. A condition control apparatus comprising in combination, a load condition sensing means, first condition control means adapted to energize condition changing means, means interconnecting said load condition sensing means and said condition control means, first timing means common to said first condition control means being operable to maintain said condition control means operable for varying periods of time proportional to values in a first range of load values indicated by said sensing means, second condition control means adapted to energize further condition changing means, coupling means, means including said coupling means interconnecting said first and second condition control means and operative to maintain said second condition control means operative when the time Y period of the periodic operation of said first condition control means has exceeded a predetermined value, means coupling said load sensing means to said second condition control means, and second timing means associated with said second condition control means and being operable to maintain said condition control means operable for varying periods of time proportional to values in a second range of load values indicated by said sensing means.

6. A condition control a aratus comprising in combination, a load condition sensing means, first condition control means adapted to energize condition changin means, means interconnecting said load condition sensing means and said condition control means. first timing means common to said first condition control means being operable to maintain said condition control means operable for varying periods of time proportional to values in a first range of load values indicated by said sensing means, second condition control means adapted to energize further condition changing means, coupling means, means including said coupling means interconnecting said first and second condition control means and operative to maintain said second condition control means operative when the time 17 period of the periodic op ration of said first condition control means has exceeded a predetermined value, means coupling said load sensing means to said second condition control means, second timing means associated with said second condition control means and being operable to maintain said condition control means operable for varying periods or time proportional to values in a second range oi load values indicated by said sensing means, and means common to said coupling means connec ed between said first and second condition control means ior maintaimng said first condition control means operative continuously when said second condition control means is operating periodically.

7. A condition control apparatus comprising in combination, a load condition sensing means, first condition control means adapted to energize condition changing means, means interconnecting said load condition sensing means and said condition control means, first timing means common to said first condition control means being operable to maintain said condition control means operable for varyin riods of time proportional to values in a first range of load values indicated by said sensing means, second condition control means adapted to energize iurtner condition changing means, coupling means, means including said coupling means interconnecting said first and second condition control means and operative to maintain said second condition control means operative when the time period or the periodic operation of said first condition control means has exceeded a predetermined value, means coupling said load sensing means to said second condition control means, second timing means associated with said second condition control means and being operable to maintain said condition control means operable for varying periods of time proportional to values in a second range of load values indicated by said sensing means, means common to said coupling means connected between said first and second condition control means for maintaining said first condition control means operative continuously when said second condition control means is operating periodically, and a plurality of further condition control means operatively connected in series with said first and second condition control means so that said devices will respond to a plurality of ranges of load conditions measured by said sensing means exceeding the ranges wherein said first and second condition control means is operative.

8. A temperature maintaining control apparatus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space and having an output which remains constant for a given heat demand, first and second electron discharge devices, means connecting said demand means to said first electron discharge device to regulate the conductivity of said first electron discharge device, circuit means including contacts of electrical switching means connected common to said first and second electron discharge devices so that said second electron discharge device is rendered operative or inoperative in time periods of varying length in accordance with the conductivity of said first electron discharge device, and means energized by the operation of said second electron discharge device for rendering heating means operative in a temperature maintainingsense.

9. A temperature maintaining control apparatus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space, first and second electron discharge devices, means connecting said demand means to said iirst electron discharge device to regulate the conductivity of said nrst electron discharge device, circuit means connected common to said first and second electron discharge devices so that said second electron discharge device is rendered operative or inoperative in time periods of varying length in accordance with the conductivity of said first electron discharge device, means energized by the operation of said second electron discharge device ior rendering heating means operative in a temperature maintaining sense, a coupling means, third and fourth electron discharge devices, means connecting said demand indicating means to said third electron discharge device for regulating the conductivity of said third electron discharge device, further circuit means connected common to said third and fourth electron discharge devices so that said fourth electron discharge device is rendered operative or inoperative in accordance with the conductivity of said third electron discharge device, further means energized by said fourth electron discharge device for rendering additional heating means operative in a temperature maintaining sense, and means including said coupling means for rendering said fourth electron discharge device efiective only when the time periods of operation of said second electron discharge device exceed a predetermined value.

10. A temperature maintaining control apparatus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space, cycling means being operable to operate in cycles of varying time periods and energize heating means, means connecting said indicating means to said cycling means to variably adjust the time periods of operation of said cycling means, an electron discharge device, said device being operable when energized to disconnect said indicating means from said cycling means, means connected common to said device and said cycling means for energizing said discharge device only when the time period of operation of said cycling means exceeds a predetermined value, and means actuated by the energization of said discharge device to alter the operation of said cycling means from cycling operation to continuous operation.

11..A temperature maintaining control apparatus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space, cycling means being operable to operate in cycles of varying time periods and energize heating means, means connecting said indicating means to said cycling means to variably adjust the time periods of operation of said cycling means, first and second electron discharge devices, said first discharge device being normally nonconducting and said second discharge device being normally conducting, a second cycling means being operable to energize further heating means in cycles of varying time periods, means connecting said second cycling means to said indicating means to variably adjust the time periods of operation of said second cyling means, means common to the acsrsas outputs of said first and second discharge devices for disconnecting said indicating means from said first named cycling means and altering the operation of said cycling means from cycling to continuous operation, means common to said first discharge device and said first named cycling means for energizing said first discharge device only when the time periods of operation of said first named cycling means exceeds a predetermined value, and means in circuit with said second cycling means for rendering said second cycling means efiective only when said first named means is operating continuously.

12. A temperature maintaining control apparatus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space, cycling means being operative to operate in cycles of varying time periods and energize heating means, means connecting said indicating means to said cycling means to variably adjust the time periods of operation 01' said cycling means, first and second electron discharge devices, said first discharge device being normally nonconducting and said second discharge device being normally conducting, a second cycling means being operable to energize further heating means in cycles of varying time periods, means connecting said second cycling means to said indicating means to variably adjust the time periods of operation of said second cycling means, means common to the outputs of said first and second discharge devices for disconnecting said indicating means from said first named cycling means and altering the operation of said cycling means from cycling to continuous operation, means common to said first discharge device and said first named cycling means for energizing said first discharge device only when the time periods of operation of said first named cycling means exceeds a predetermined value, and means in circuit with said second cycling means for rendering said second cycling means eflective only when said first named means is operating continuously.

13. A temperature maintaining control appa ratus comprising in combination, demand indicating means being operative to indicate the amount of heat needed to maintain a constant temperature in a given space, cycling means be ing operable to operate in cycles of varying time periods and energize heating means, means connecting said indicating means to said Cycling means to variably adjust the time periods of operation 01' said cyling means, first and second electron discharge devices, said first discharge device being normally nonconducting and said second discharge device being normally conducting, a second cycling means being operable to energize further heating means in cycles of varying time periods, means connecting said second cycling means to said indicating means to variably adjust the time periods of operation of said second cycling means, means common to the outn ts sa d first and second discharge devices for disconnecting said indicating means from said first named cycling means and altering the operation of said cycling means from cycling to continuous operation, means common to said first discharge device and said first named cycling means for energizing said first discharge device only when the time periods of operation of said first named cycling means exceeds a predetermined value, means in circuit with said second cycling means for rendering said second cycling means eflective only when said first named means is operating continuously, and further means actuated by said second cycling mean for rendering said second cycling means inci- 'fective and said second discharge device nonconducting when said indicating means indicates a demand less than that indicated when said second cycling means was rendered effective.

14. A temperature control device comprising in combination; heat demand indicating means having an output signal whose magnitude corresponds to the amount of heat required to maintain a constant temperature within a given space; a plurality of heat energizing circuit means, each of said means comprising first and second electron discharge devices having anodes, cathodes and control electrodes, a source of power, a resistor, a condenser, means connecting said resistor and said condenser in parallel, mean connecting said condenser in a closed series circuit with said source of power and said first discharge device so that said first discharge device is operable when conducting to charge said condenser, means connecting said indicating means to the control electrode of said first discharge device to regulate the fiow of current through said series circuit, a second resistor, a second condenser, means connecting said second resistor and ondenser in a control electrode cathode circuit of said second discharge device and to said first named condenser so that said second condenser will be charged by said flrst named condenser at a rate determined by said second resistor, a relay operable when energized to energize heating means, means connecting said relay in the conducting circuit of said second discharge device so that said relay is energized when the current fiow through said second discharge device exceeds a predetermined value, further mean associated with said relay for discharging said second condenser at a predetermined rate so that said relay is energized and deenergized for time periods determined by the charging and discharging of said second condenser, coupling means, means connecting said coupling means between each of said energizing circuit means, and timing means common to each of said coupling means being operable to maintain all energizing circuit means preceding said coupling means operable continuously and the energizing circuit succeeding said coupling means operable in accordance with the signal from said indicating means when said indicating means has an output within a predetermined range.

15. A condition control apparatus for use with a load condition sensing means, comprising, a plurality of interconnected condition control devices each adapted to energize periodically or continuously means for maintaining a condition at a desired value, each of said control devices including circuit means controlled by said load demand sensing means modulatingiy varying the periodic operation of said device, means for connecting each of said condition control devices to the sensing means, a plurality of coupling means, and means connecting a separate one of said coupling means between each of said condition control devices and being operable to energize each succeeding of said condition control devices periodically when the condition control device preceding said coupling means is operating continuously.

16. A condition control apparatus for use with a load condition sensing means, comprising, first control means adapted to energize means for assasas maintaining a controlled condition within a desired range, means for interconnecting the load condition sensing means and said condition control means, timing means common to said first condition control means being operable to maintain said condition control means operative for varying periods 01' time proportional to the load indicated by the sensing means, second condition control means adapted to energize further means for maintaining a condition within a desired range, coupling means, and means including said coupling means interconnecting said first and second condition control means and operative to maintain said second condition control means operative when the operational time period of the periodic operation of said first condition control means has exceeded a predetermined value.

17. A temperature maintaining control apparatus for use with a demand indicating means which indicates the amount 01' heat needed to maintain a constant temperature in a given space and having an output signal which remains constant for a given heat demand, comprising, 'first and second electron discharge devices, means for connecting the demand means to said first electron discharge device to regulate the conductivity of said first electron discharge device, circuit means including contacts of electrical switching means connected common to said first and second electron discharge devices so that said second electron discharge device is periodically rendered operative at a predetermined rate in accordance with a predetermined fixed degree oi conductivity of said first electron discharge device, and means energized by the operation of said second electron discharge device i'or rendering heating means operative in a temperature maintaining sense.

18. In a control apparatus for controlling the operation at least two condition changing devices in accordance with a control signal which varies with load demand, the combination comprising, first means for effecting periodic or continuous operation of the changing devices in a sequential manner so that one of said devices.

will be operating continuously and the other of said devices will be operating periodically, said periods of periodic operation being of increasing length for increasing load, circuit means connected to said first means for causing said other 01' said devices to become operative periodically when the controlling signal reaches a first value, and means including said circuit means for causing said first means to discontinue periodic operation of said other device and efiecting periodic operation of said one device when the controlling signal changes from said first values to'a second value.

19. Apparatus for controlling a condition having an input control signal which varies with load demand and which is adapted to control a plurality of condition changing means, the combination comprising, a first control means for controlling one of the condition changing means, timing means whose timing operation is con trolled by the input signal to said apparatus connected in controlling relation to said first control means causing said control means to energize the associated changing means for time periods of variable length, a second control means for controlling a further of said condition changing means, and means including said timing means connected to said first and second control means for maintaining said second control means inoperative when said first control means is operating periodically until the time periods of operation of the first control means exceeds a predetermined value when the second control means is rendered operative periodically and the first control means operative continuously.

20. Apparatus for controlling a condition having an input signal which varies with load demand and which is adapted to control a condition changing means, comprising in combination, a control means which is adapted to effect operation of the condition changing means, and timing means whose timing operation is controlled by the magnitude of the input signal to the apparatus connected to periodically energize said control means, said timing means comprising a first electron discharge device whose conductivity is controlled by the input signal, a condenser connected to said device and receiving a charge which varies with the conductivity of said first device, a second electron discharge device connected in controlling relation to the input 01' said second device, and means including said control means alternately connecting said timing condenser to said first named condenser and to a discharging circuit so that said second device will be operative for periods of variable length dependent upon the value of the input signal.

GENE 'I'. GADDIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

